1. Field of the Invention
The present invention relates generally to integrated circuit fabrication equipment, and more particularly but not exclusively to magnetron sputtering.
2. Description of the Background Art
Magnetron sputtering, in general, is well known in the art of integrated circuit fabrication. A magnetron sputtering apparatus includes a target comprising a material to be deposited on a substrate. The substrate, which may be a semiconductor wafer, is located a distance away from the target. To coat the substrate with the target material, a plasma of a gas suitable for sputtering is maintained between the target and the substrate. When ions of the sputtering gas hit the target, atoms of the target material are dislodged from the target and onto the substrate.
FIG. 1A schematically shows an example magnetron sputtering apparatus 100. Apparatus 100 includes a target 101 and a magnetic circuit comprising magnets 121, 122, and 123. Magnets 121, 122, and 123 and their respective magnetic fields 104 (i.e., 104-1, 104-2, . . . ) are cylindrically symmetric about a center line 112. A plasma loop 105 is maintained to sputter a target 101, which is a planar target in this example. A “plasma loop” comprises plasma formed in a region or path. In apparatus 100, magnets 121, 122, and 123 are configured such that magnetic fields 104 confine plasma loop 105. The effectiveness of the confinement depends on the strength of magnetic fields 104. However, in apparatus 100, electrons in plasma loop 105 have a tendency to diffuse to regions of weak magnetic fields and escape to the chamber walls. This makes it relatively difficult to maintain a high density plasma in front of target 101.
The sputtering track on a target generally follows the shape of the plasma loop formed over the target. For example, because ions from plasma loop 105 sputter target 101, target 101 is eroded only in areas under plasma loop 105. FIG. 1B is a plan view schematically showing a ring-shaped sputtering track formed by plasma loop 105 on target 101.